local bit = require('bit')

local function opcode(id, name, a, b, c, metamethod)
    return {
        id=id,
        name=name,
        a=a,
        b=b,
        c=c,
        methametod=metamethod,
    }
end

local function gen_opcodes(tbl)
    res = {}
    for i = 1, #tbl do
        res[tbl[i].id] = {
            name = tbl[i].name,
            a = tbl[i].a,
            b = tbl[i].b,
            c = tbl[i].c,
            metamethod = tbl[i].metamethod,
        }
    end
    return res
end

local Mode = {
    none = 0,
    dst = 1,
    base = 2,
    var = 3,
    rbase = 4,
    uv = 5,
    lit = 6,
    lits = 7,
    pri = 8,
    num = 9,
    str = 10,
    tab = 11,
    func = 12,
    jump = 13,
    cdata = 14,
    max = 15,
    none = 15, -- same as max
}

local Metamethod = {
    index = 0,
    newindex = 1,
    gc = 2,
    mode = 3,
    eq = 4,
    len = 5,
    lt = 6,
    le = 7,
    concat = 8,
    call = 9,
    add = 10,
    sub = 11,
    mul = 12,
    div = 13,
    mod = 14,
    pow = 15,
    unm = 16,
    metatable = 17,
    tostring = 18,
}

local Opcodes_defs = gen_opcodes {
    opcode(37, 'POW', Mode.dst, Mode.none, Mode.lits, Metamethod.none),
    opcode(41, 'KSHORT', Mode.dst, Mode.var, Mode.var, Metamethod.pow),
    opcode(75, 'RET0', Mode.rbase, Mode.none, Mode.lit, Mode.none),
}

local function decode(ins)
    -- TODO: endianess
    local id = bit.band(ins, 0xff)
    local a = bit.band(ins, 0xff00) / 0x100
    local b = bit.band(ins, 0xff0000) / 0x10000
    local c = bit.band(ins, 0xff000000) / 0x1000000
    local d = bit.band(ins, 0xffff0000) / 0x10000
    return {
        id = id,
        a = a,
        b = b,
        c = c,
        d = d,
    }
end

return {
    defs = Opcodes_defs,
    decode = decode,
}